Oh, I also know of 2 others with 05 WHITE GM trucks supposidly JUST LIKE mine, one weighs 7100 lbs, the other 7600 lbs. I have a mid trim 4x, the light is a basic pkg rwd, the HEAVY dude, a full on leather 4x4. That is what, 500 lbs between three trucks, supposedly all the same!
The first dmax that was on the road that folks saw, pulling a trailer around the US telling about that motor, was a reg cab dually, pulling a 20K trailer, and it weighed 6000 lbs with the driver and an alternate driver person in it! I fully believe the OP has a dually truck that weighs 6000 lbs! I could do it with a 2013 or a 14 frankly!
Marty